1. Field of the Invention
This invention relates to a piezo-electric actuator control method and device for performing the control of a piezo-electric actuator which drives a variable wavelength filter used in a wavelength division multiplexed optical communication system.
2. Description of Related Art
Conventionally, control of a piezo-electric actuator using such piezo-electric element disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 63(1988)-283180 "a piezo-electric actuator having a displacement sensor", Japanese Patent Application Laid-Open No. Hei 2(1990)-111273 "piezo-electric actuator driving device", and Japanese Patent Application Laid-Open No. Sho 63(1988)-283087 "driving method of a piezo-electric element" has been known.
In a conventional example disclosed in Japanese Patent Application Laid-Open No. Sho 63-283180, a displacement sensor is provided to a piezo-electric actuator, and the displacement sensor is used for feed back control.
In a conventional example disclosed in Japanese Patent Application Laid-Open No. Hei 2-11273, the voltage to be applied to a piezo-electric actuator is prescribed to zero, and thereafter a driving voltage is applied to the piezo-electric actuator.
Further, in a conventional example disclosed in Japanese Patent Application Laid-Open No. Sho 63-283087, the maximum voltage is applied to a piezo-electric actuator, and thereafter a driving voltage is applied to the piezo-electric actuator.
However, the conventional example disclosed in Japanese Patent Application Laid-Open No. Sho 63-283180 requires a control system comprising a displacement sensor, displacement detecting circuit, and feedback circuit, and therefore the structure is complex.
The conventional examples disclosed in Japanese Patent Application Laid-Open No. Hei 2-11273 and Japanese Patent Application Laid-Open No. Sho 63-283087 involves the adverse effect of residual hysteresis which causes inaccurate controlling of displacement position, and therefore there is room for further improvement.